The present invention refers to a convergent-divergent nozzle of variable geometry capable of orienting the flow of gas, for a gas turbine engine, used as a means of propulsion in aviation.
More specifically, in a preferred application, the nozzle to which the present invention relates is of the axisymmetric type, comprising a convergent zone followed, in the direction of flow, by a divergent zone, both of which are formed by master petals distributed circumferentially around the longitudinal axis of the engine and connected to each other by articulations and by slave petals, also connected together by articulations and distributed circumferentially around the longitudinal axis of the engine. The convergent zone defines an A8 throat of variable area. The divergent zone, which is also of variable geometry, may be actuated so as to orient the flow of gas and, therefore, the thrust in any direction on a cone directed around the longitudinal axis of the propulsor.
Maneuverability of airplanes is essential. Maneuverability has been obtained up to now by aerodynamic forces, but it can be substantially improved by changing the orientation of the flow from its normal axial direction of actuation.
Orienting the flow of gas has been used for many years in rocket motors. In those engines, the systems are much simpler, since their nozzles are of constant geometry.
Convergent-divergent nozzles of variable geometry have relatively recently been introduced in supersonic planes driven by turbojet or turboprop engines. In this class of nozzles, the systems for orienting the flow are not yet in an operational stage, but are instead in the experimental or developmental phase. Those of the two-dimensional type in which the flow is oriented only in one plane are in the most advanced state.
It is of particular advantage to orient the flow in nozzles with axial symmetry since the direction of the flow can then be varied in any axial plane, with the pitch and yaw planes being particularly important.
Various prior patents cover mechanisms for orienting the flow in this type of nozzle, since it is theoretically possible to effect this in different ways, although it is very difficult for the mechanisms not to have a high degree of complexity.
To orient only the divergent zone of the nozzle downstream of the A8 throat area has the advantage that the disturbances induced by the orientation are not transmitted upstream of the engine and that the sealing of the spaces between the different moving parts is simplified. There still remains the problem of the seal between divergent master petals during the orienting of the flow. With regard to this, reference should be had to U.S. Pat. No. 4,994,660 and to Spanish Application No. 9200369 of 1992, which disclose different embodiments of nozzles in which only the divergent zone, or a part of it, respectively, is oriented.
In order to seal the spaces between divergent master petals there are various solutions, such as those contained in U.S. Pat. Nos. 4,690,330, 4,662,566, 5,039,014 and 5,076,496, and Spanish Applications Nos. 9200369 of 1992, 9202157 of 1992, and No. 9301991 of 1993.
Spanish Patent Application No. 9200369 of 1992 describes an orientable axisymmetric nozzle of variable geometry for gas turbine engine. This nozzle consists of a convergent zone and a divergent zone, both of which are formed of master petals and slave petals distributed circumferentially around the longitudinal axis of the engine. Control and outer radial support means are provided for regulating the throat area, and control means is provided for regulating the orientation of the flow. Its novel feature is the fact that the variation of the A8 throat area and the orientation of the flow are effected by a single control system which is formed of three annular parts which are concentric to each other and to the longitudinal axis of the engine and by a plurality of linear actuators articulated at their upstream end to the fixed structure of the engine.
The annular parts are connected to each other and to the fixed structure of the engine by articulation elements and guide devices. These permit the joint axial displacement of the three annular parts by the same amount with respect to the fixed structure of the engine, and permit a movement of relative rotation of the intermediate and outer annular parts with respect to each other and with respect to the inner annular part. This thus permits the inclination of the outer annular part in any direction, with a center of rotation on the longitudinal axis of the engine.
The convergent master petals are connected at their upstream ends to the inner annular part by cylindrical articulations which are tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and is located in a theoretical plane perpendicular to the longitudinal axis of the engine. The outer annular part, in turn, is connected by spherical articulations to the downstream end of the linear actuators.
The mechanism for variation of the A8 throat area is formed of a lever which is firmly attached to the fixed structure of the engine on which there rests and rolls a roller which is mounted, with the possibility of free rotation, on the corresponding convergent master petal.
The master petals of the divergent zone are subdivided transversely into two sections which are connected together by a cylindrical articulation, the axis of which is perpendicular to the axis of articulation between the master petals of the convergent and divergent zones. The downstream section is connected to the outer annular part by a bar which is connected to the downstream section by a spherical articulation, and is connected to the outer annular part by a cylindrical articulation which is tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to such longitudinal axis.
The upstream section of each divergent master petal is connected, at its upstream end, to the corresponding convergent master petal by a cylindrical articulation, tangential to a theoretical circumference which is concentric to the longitudinal axis of the engine and located in a theoretical plane perpendicular to such longitudinal axis.
Spanish Patent Application No. 9202157 of 1992 describes a design of a divergent slave petal for sealing of longitudinal space between contiguous divergent master petals. The geometry of the longitudinal spaces between divergent master petals is changed during the orientation of the flow, changing from an approximately rectangular form to that of an adjusted surface, the sides of which are no longer parallel.
This reference proposes converting every divergent slave petal into a deformable structural unit of minimum stiffness in torsion, which is formed of a base plate and a plurality of discrete transverse elements inserted in the base plate. The base plate imparts axial stiffness to the unit, serving as element for bearing the axial forces due to the flow of gas, the cooling air, and the inertia forces, but presenting minimum ability to transmit transverse forces. On their part, the discrete transverse elements lack an ability to transmit torsion, but they do transmit the transverse forces and the shearing forces imposed both by the flow of gas and by the divergent master petals to which the gas pressure exerted on the base plate bearing the axial forces is transmitted.
Thus, Spanish Patent Applications 9200369 and 9202157 of 1992, disclose a mechanism capable of orienting the flow of gas by acting solely on a part of the divergent zone of the nozzle with a suitable sealing of the longitudinal space between contiguous divergent master petals. U.S. patent application Ser. No. 08/232,706, filed on even date herewith in the names of Jose Rivacoba Urruola and Jose Ignacio Ibarreche Mendia and entitled "Divergent Master Petal for Orientable Nozzles of Variable Geometry Intended for Gas Turbines", the entire disclosure of which is incorporated by reference herein, describes a divergent master petal which makes it possible to increase the maximum angle of orientation of the flow with respect to that obtainable with the embodiments set forth in Spanish Patent Applications Nos. 9200369 and 9202157.
In orienting the divergent zone of the nozzle, the divergent master petals, as described in Spanish Patent Application No. 9200369, are forced to move in radial and tangential directions with respect to the longitudinal axis of the engine. The maximum angle of orientation of the divergent zone for a given A8 throat area is limited by the interferences between master and slave petals in zones near the A9 exit area. As indicated previously, Spanish Patent Application 9202157 of 1992 proposes converting the divergent slave petal into a deformable structural unit of minimum stiffness in torsion, which is formed by a base plate bearing the axial forces and with minimum capacity to transmit transverse forces. The base plate includes discrete transverse elements with capacity to transmit the transverse forces and the shearing forces imposed both by the flow of gas and by the divergent master petals. If the inner surface of the divergent master petals, which is the surface in contact with the flow of gas, is flat, the maximum angle of orientation of the flow is determined by the interference in zones close to the A9 exit area of the inner surface with the discrete transverse elements because, in this case, the longitudinal edges of the base plate do not rest on the inner surface of the divergent master petals, a longitudinal opening appearing which permits the passage of the gases to the outside.
In order to solve this problem, the abovementioned U.S. Application filed on even date herewith proposes a divergent master petal which has an inner surface, which is in contact with the flow of gas and is of a shape that is variable between two cross sections, one of them straight, so as to coincide with or be close to the upstream end transverse edge of the petal, and the other one curved convexly so as to coincide with or be close to the downstream end transverse edge of said petal, the convexity of the curvature being directed toward the inside of the engine. The transmission between the two cross sections is effected gradually and smoothly in order to permit continuous contact of the divergent slave petal with the inner surface.